The present invention relates to vehicles, their connection to the ground and the measurement of the forces exerted through the roadway on the tires of the vehicles.
The present invention also relates to various electronic assistance devices used, for example, for the antilock brake control of a vehicle or the antiskid control of the driving wheels, the control of the course of a vehicle, or indeed other forms of control or monitoring, such as that of the tire pressure.
In order to control the behavior of a vehicle, the attempt has been made to determine certain running parameters. Thus, in order to reduce longitudinal sliding of the wheels, systems for limiting slide (ABS, ASR) have been developed which are capable of modifying the torque transmitted to the wheel from the engine or the brake as a function of the slide deduced from the variations in the speed of rotation of each wheel. It has also been proposed that the torsion (angular circumferential deformation) of the side walls of a tire be measured in order to determine the variations in the torque transmitted to the roadway. This measurement, which is more direct than deduction from the variation in the speed of rotation, may allow finer regulation of the slide limitation systems.
Also known are systems (such as ESP) which act on the brakes or the driving power applied to the wheels to ensure that the course desired by the driver is indeed followed by the vehicle. For this, the yaw speed (the speed of rotation of the vehicle about a vertical axis), the running speed, the transverse acceleration of the vehicle and the angular position imposed on the steering wheel by the driver are generally measured simultaneously.
The invention takes as its starting point the observation that all the forces exerted through the roadway on the vehicle are transmitted through the wheels. The accelerations undergone by the vehicle depend on the overall effect of these forces. Thus, determining these forces as a whole could allow the different sensors mentioned above to be dispensed with. To do this, the known methods (see above) may allow the longitudinal forces to be known. The vertical forces may also be measured by various known methods. To determine in a complete manner the overall effect of the forces exerted through the roadway on the vehicle, all that remains to be known are the transverse forces. It is an object of the invention to determine these in simple and reliable manner.
The method according to the invention is based on the experimental finding that the transverse forces acting between the tread of the tire and the roadway result in a substantial and reproducible deformation in the form of a circumferential torsion of the side walls of the tires. If this angular circumferential deformation is successfully measured in isolated manner in real time, it may allow the direction and intensity of the transverse forces acting on the tire to be known at any given moment.
The invention relates to a method for determining a transverse component of a resultant of forces exerted through the roadway on an contact area of a tire, the method being characterized in that the transverse component is deduced from at least one measurement of the angular circumferential deformation in at least one first side wall of the tire at a first fixed point in space which is located at an azimuth along the circumference of the tire which differs from the azimuth of the center of the area of contact and differs from the azimuth of the point opposite the center of the area of contact.
The invention also relates to a method as described above, characterized in that such a measurement is performed respectively in each side wall to obtain a first measurement and a second measurement and the transverse component is deduced from the difference between the first and second measurements.
The method according to the invention also makes it possible to deduce from the measurement of the torsion of the side walls of the tires the other (or one of the other) components of the resultant of the forces exerted on the area of contact, that is to say not only the transverse forces (called the “y” forces) but also the longitudinal forces (called the “x” forces) and the vertical forces (called the “z” forces) as are exerted between the tire and the roadway.
The invention thus also relates to a method as described above and characterized in that there is furthermore performed a such measurement in the first side wall at a second fixed point in space which is distinct from the first point and located at an azimuth substantially opposite the first point in order to obtain a third measurement, and in that a longitudinal component of the resultant of forces exerted through the roadway is furthermore deduced from the sum of the first and third measurements.
Preferably, the invention relates to a method as above where a vertical component of a resultant of forces exerted through the roadway is furthermore deduced from the difference between the third and first measurements and a contribution of the transverse component.
These different components participate differently but simultaneously in the deformations of the tire and in particular in the tangential displacement of the crown (or tread) with respect to the hook zone (or bead) on the rim. This angular circumferential deformation (or torsion of the side walls), which is more or less homogeneous along the circumference of the tire, takes the form of a deflection of the carcass reinforcements in the case of tires with a radial carcass. This is often called a “deradialization”. The method according to the invention does not, however, apply only to tires with a radial carcass, but, rather, the behavior of radial reinforcements, that is to say, those substantially parallel to the radii of the tire, enables a “practical illustration” to be given.